A man who aimed a laser light at the Nelson Marlborough Rescue Helicopter on its return from a late-night search was not operating under the cover of darkness as he thought.

The pilot and crewmen on the helicopter, returning to base at Nelson Airport around 2am yesterday, had a laser light shone at them. It is a criminal offence under civil aviation law because of the danger it presents to pilots.

Nelson Marlborough rescue helicopter pilot Jarrod Colbourne said today the pilot and crewmen were returning from the Mt Owen search for tramper Alistair Levy when the incident happened.

They were able to pinpoint the property and ultimately the man responsible by using the chopper's onboard Forward Looking Infra Red Unit.

"They were also able to use the unit, which is used to locate any heat source during a search, and the pilot could see the person walking around the balcony of the house," Colbourne said.

Pilot Tim Douglas-Clifford said onboard intensive care paramedic Jon Leach, who was operating the infra red unit and therefore not wearing night-vision glasses, was most affected by the laser strike.

"We were able to pinpoint the property straight away," he said.

Douglas-Clifford contacted the police, then hovered over the property for several minutes until they arrived at the house.

Police said today a man had been summonsed to appear in the Nelson District Court in relation to the incident.

The Civil Aviation Authority said recently that laser illumination of aircraft was an offence because it could cause distraction, disorientation and discomfort for pilots resulting in a potentially hazardous situation during critical phases of flight.

Anyone who pointed a laser at an aircraft could be charged under the Civil Aviation Act with causing unnecessary danger. The maximum penalty for this offence was up to 12 months' imprisonment or a fine of up to $10,000.

The Nelson Marlborough Rescue Helicopter said the last 48 hours had been extremely busy with a total of eight missions flown, including medical, accident and search and rescue missions.